The subject matter disclosed herein relates to medical imaging systems and, in particular, to addressing the power requirements of a magnetic resonance imaging system.
Non-invasive imaging technologies allow images of the internal structures or features of a patient to be obtained without performing an invasive procedure on the patient. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of X-rays through the imaged volume or the gyromagnetic properties of materials within the imaged volume, to acquire data and to construct images or otherwise represent the observed internal features of the patient.
For example, in general, magnetic resonance imaging (MRI) examinations are based on the interactions among a primary magnetic field, a radiofrequency (RF) magnetic field, and time varying magnetic gradient fields with a gyromagnetic material having nuclear spins within a subject of interest, such as a patient. Certain gyromagnetic materials, such as hydrogen nuclei in water molecules, have characteristic behaviors in response to external magnetic fields. The precession of spins of these nuclei can be influenced by manipulation of the fields to produce RF signals that can be detected, processed, and used to reconstruct a useful image.
The magnetic fields used to generate images in MRI systems include a highly uniform, static magnetic field that is produced by a primary magnet. A series of gradient fields are produced by a set of gradient coils located around the imaging volume in which the subject is placed. The gradient fields encode positions of individual plane or volume elements (pixels or voxels) in two or three dimensions. An RF coil is employed to produce an RF magnetic field. This RF magnetic field perturbs the spins of some of the gyromagnetic nuclei from their equilibrium directions, causing the spins to precess around the axis of their equilibrium magnetization. During this precession, RF fields are emitted by the spinning, precessing nuclei and are detected by either the same transmitting RF coil, or by one or more separate coils. These signals are amplified, filtered, and digitized. The digitized signals are then processed using one or more algorithms to reconstruct a useful image.
MRI images provide a variety of benefits and may be particularly useful for certain imaging contexts, such as acquiring images of soft tissues in the human body. However, the various components and sub-systems of a typical MRI system, such as the gradient drivers, the RF transmit chain, the RF receiver, and the patient handling system may impose considerable, but transitory, power requirements on the system. For example, while the system power requirements are minimal when no scan is being performed, during certain scan protocols the momentary power requirement becomes extremely high, resulting in high currents drawn from the AC mains which typically power the system. Thus, in practice MRI systems may have a high peak-power to average-power ratio. The peak power requirement drives the size of the electrical installation and, hence, the provided electrical installation is typically oversized relative to average load. This scenario may become more pronounced in future as the gradient power requirements are likely to increase significantly with wide bore MRI systems used for neurological scans, which may lead to the peak power requirement during scanning increasing by multiple folds.